Since the back was a little better, after I left the chiropractor yesterday I headed north to take care of some things, one of which was to stop and pick up this engine case to patch up for my buddy. It's from a BSA Bantam he's working on for someone. It's hard to tell from the crappy photo but it's just a little spot on the outside of the dowel pin. Only about five minutes work.

The case has a lot of zinc in it - I could tell right away from the color of the arc. The more zinc the more difficult it is to get a good looking job. You have to be patient. If you overheat it the zinc will bubble up through the weld and leave holes in the finished weld. Plus it never comes out shiny bright like the pieces in the top two photos. You can usually look at the casting and have a pretty good idea of the alloy before you start. The good aluminum alloy like A-356 will be closer to white in color, where the zinc is more of a gray - or would that be grey since it's from England? The casting shape will also give you an idea. The more intricate the shape you can count on more zinc in the mix. The zinc retains the heat better while pouring to insure the material flows to all parts of the die. With sand casting, you usually see a nicer grade of aluminum, at least as far as motorcycle parts go. On some things there's a noticeable difference in weight as well, zinc being heavier. You will also run across some magnesium once in a while like on the engine side covers on the early Elsinores. They even cast a warning right into the part to let all the jack leg weldors know before attempting a repair. In all the years I've been puttering around with motorcycles, I haven't welded too many things on Brit bikes. I'm not sure if that says something about the quality of the bikes or just the people I run with.

2 comments:

Glad you found it useful. Maybe I should do a follow-up with more specific welding information - type of filler rods, weld prep, etc. There was a real good article in the Welding Journal not too long ago about figuring out the type of aluminum and welding procedures. Might be useful for readers.

Regardless, it's good that I'm getting out into the shop, using the tools and actually have something worth posting.